The present invention is directed to electrical assemblies configured according to assembly methods, and especially to electrical assemblies and methods effecting inter-part electrical coupling in an assembled state.
Some electrical assemblies are designed to effect electrical contact between or among respective parts by pressure contact between or among parts during an assembly process that results in an assembled configuration of parts. By way of example and not by way of limitation, RF (radio frequency) microwave integrated circuit (MIC) modules are bolted into housings using mounting screws. A MIC module typically includes a two-conductor microstrip transmission line for conveying microwave signals. Establishing a required RF ground under the microstrip transmission line relies upon the pressure contact established between the MIC module and the housing as the MIC module is bolted into the housing. Because of surface irregularities and flatness issues regarding both of the parts—the housing and the MIC module—intermittent contact may be established at the interface between the housing and the MIC module. An intermittent contact interface may cause output power perturbations during operation of the assembly.
The primary conductor in the microstrip transmission line is typically a gold trace printed on dielectric material supporting the microstrip transmission line. Representative materials employed for such dielectric material includes, by way of example and not by way of limitation: alumina, Rogers 4003, TMM-10, duroid and other dielectric materials known in the art of MIC modules. By way of further example and not by way of limitation, the dielectric material may be attached to a gold or silver plated conductive header such as kover, silvar, stainless steel or another header material known in the art of MIC modules. The header material may be employed to act as the second conductor in the two-conductor microstrip transmission line.
Different microstrip modules may be electrically connected together via a gold ribbon that is welded or soldered between the respective microstrip transmission lines that are printed or otherwise affixed to the dielectric material. The header may typically be employed as a ground conductor and may be bolted to the housing. Bolting the parts together is preferred some assemblies for both mechanical and electrical reasons. However, bolting the header to the housing is known to experience the problem of intermittent contact between the housing and the header. Intermittent contact is caused by irregularities in the surface finish of the bottom of the header and the housing surface that contributes to less than ideal flatness of the interface between the header and the housing surface. Small high points, often of microscopic scale, make contact at the two surfaces presented at the interface between the housing and the header. These high points may move as the assembly is thermally cycled or vibrated. This movement may cause the inter-part contact points to move or shift. This moving or shifting action causes intermittent contact between parts at the header-to-housing interface that is manifested in perturbations shown in output power plots over a range of temperature.
This intermittent contact, sometimes referred to as “ground jumps”, is often found in temperature cycling and may require extensive troubleshooting and rework to eliminate. Usually, these power jumps or perturbations are discovered during RF performance testing that typically involves temperature cycling. Troubleshooting and fixing the power jumps is very time consuming and costly as they require disassembly and reassembly using additional gold conducting ribbons between the header-to-housing interface.
One solution employs gold ribbon that is place between the header-to-housing interface underneath the RF transmission line to create a “gasket” affect so that the carrier (i.e., the microstrip transmission line) establishes a pressure contact in the region of the gold ribbon. Size and placement of ribbon may be variable geometry of the header-to-housing interface.
Incorrectly placed or incorrectly sized ribbons may lead to physical damage to solder or epoxy bond lines between the substrate and carrier or may lead to physical cracking of the substrate. Sufficiently reducing this intermittent contact problem to assure reliable performance by the header-to-housing interface usually involves a plurality of iterations of RF performance testing or temperature cycling.
There is a need for an assembly and a method for effecting the assembly that establishes a substantially continuous electrical interface between parts of the assembly in response to an urging together of the parts of the assembly.